Filling up fuel tank to full after use?

[frogfuzz]

Hi All

I have seen it said on TV that you should fill up your fuel tank to full after use to stop condensation gathering in it. Is this true?

I have a 100l tank in the boat, and so filling it costs me a bit of $$. I use the spare fuel in the car over the next week or so inbetween trips. I fill the thing up before use, but my boat motor uses next to nothing. I have also been told that fuel goes "stale", hence I use it in the car.

Should I fill up the boat tank after use to stop condensation and just leave it full?

Thanks

Ian B

[Noelm]

I guess this is one of those old "it can't hurt" things, a lot of people do this, I tend to keep the tanks sort of half and above, but it does make sense (I guess) but I have never really had any problems in 30 years of under floor tanks, remember that if your tank is full, even though it may cost a bit (I have 2 X 250 litre tanks) you still have the fuel to use, it does not matter whether you fill the Boat, then use it in your car and not pay for the Car for a week, or keep it in the Boat and pay for the Car, does not matter, you still have to buy and use the same amount.

[ROBENDOG]

There was a recent thread discussing stale fuel, and I raised this issue as I had been told to fill the tank when not using the boat to reduce condensation..

Basically the replies outlined that if you have a decent fuel filter then condensation is no issue as water will be filtered out.

On the stale fuel side......replies indicated that fuel will go stale in your fuel tank in about 1 month placing your engine at risk. Apparently fuel will last 12 months in sealed containers (jerry cans).

After reading the replies on this thread, and doing a little internet research myself, I no longer fill my tank at the end of the day. I will be investing in a higher quality fuel filter and filling on the way to the ramp.

Have a read through the stale fuel thread for yourself and see what you think.

Ben.:)

[Kleyny]

mmm do you keep your car full all the time if it stands for long periods?


neil

[ozscott]

Ditto Robbendog - I used a very fine filter and water trap and condensation is therefore not an issue - old fuel is, so sometimes I cheat and when I go to fill up if the fuel remaining is say a third I use the highest octane fuel to fill up meaning that when its all in there together the octane is back down to about what outboards like - ie lower octane. If you use standard octane in such circumstances the whole lot might be too low if the fuel is 2-3 months or more old and you risk pinging and a hole in a piston...but if the fuel is getting too old I drain to be on the safe side and use it in the ridey

Cheers

[mirage]

There is an excellent article in the latest Australian Fisherman and Boatowners (F&B) magazine. Well worth a read.
Too much detail to go into fully but the Senior Fuel Chemist at BP states "High octane (95 & 98) fuels should NOT be used in outboard tanks. Only normal unleaded should be used"
He recommends keeping boat tanks one third full to stop condensation and add at least one third of fresh fuel before going boating. Do NOT use fuel with Ethanol added. "Normal life of fuel in a boat tank is about 3 weeks (much less in high temperatures) after which the fuel starts to get too heavy for the fuel system". (the "heavy" part is explained in the article).

Lots to consider there!

[stevedemon]

Hi frogfuzz
Mate i was informed by the mechanic's years ago never fill the tank until you are ready to use it.
as it may be a while before you go out, if it sits for to long an you are worried about condensation then place a litre of mentho in the tank.

this will mix the condensation with no effects on the motor the same as you can also go a little further an place a water trap filteration system on the vessel, but to be safe do not fill unless you know you are using vessel with in a time period.

Cheers
Steve

[scoota]

Bad idea FF, as mirage has stated a read of F&B is pretty close to the mark.

Petrol breaks down full stop. More quickly the higher the octane and can crystalize in carbies and injection systems causing problems if you are not using your outboard at least once a week.

Keep your tank a third full and top up before heading out so as mix old fuel with new stuff and run it low before servicing so as to have fresh fuel supplying the motor after a full service.

Scoota....

[Outsider1]

The BP Chemist also indicated that fuel stablisers do work, and are worthwhile using. For commercial reasons he would not recommend brands but you got the feeling that he was talking about the well know ones put out by the outboard manufacturers

Cheers

Dave

[ozscott]

what is the well known one and were do you get it?

[Outsider1]

what is the well known one and were do you get it?

Hi ozscott,

I use OMC 2 + 4 Conditioner, but I believe Yamaha, Mercury etc all make their own versions. Any chandlery or boat yard should carry it. Just ask for Fuel Conditioner.

Cheers

Dave

[ozscott]

Cheers Dave

[frogfuzz]

Hi All

Thanks for all your replies. My rig has a water trap thingy on it (yes I'm not all that technical!), so I will continue to siphon it out and use it in the car inbetween trips (with the way fuel is rising in $$ these days it actually saves money buying that much at a time)

I will also have a read of that magazine mentioned above.

Thanks all

Ian B

[Mindi]

Further to Mirage post above there is also an article in last month Trailerboat Fisherman saying much the same thing...the idea of condensation in a partly full tank is correct...but when you do the calculations (as he does) it appears that the amount of water is insignificant and the risk of water is much higher from other sources like the servo underground tank and rain getting in thru poorly sealed filler caps...good article....

why is standard the go for modern outboards and not 95/98..?

[BM]

I tell my customers that they are better off planning their fuel use so they are not stuck with stale fuel on a regular basis. This means definitely not having a full tank of fuel at all times. Better to have none or next to none.

A water separating fuel filter will take care of any condensation that does end up in the tank so condensation is not an issue worth considering. Stale fuel is far more of a problem.

So keep your tank near empty and fill it when you are going to use. Your water sep filter will be changed annually when you have the engine serviced.

Cheers

[sheridan]

I have a 40ltr stainless tank in my boat with a water trap filter i usually take 20ltrs spare fuel i used to take it in a 20 ltr container and if i needed a bit to get home i would have to mix the lot as it is a 2stroke but i found these 10 ltr steel jerry cans at repco and they fit nicely one either side of my tank and if need be i can mix 10 ltrs or 20 ltrs accurately . I too put my unused mixed fuel in my old nissan no problems


Geoff